Ion exchange membrane water electrolyzers for producing hydrogen and oxygen from water have been known for more than 20 years. The electrolyzer's components typically include chambers for the introduction of water and the removal of hydrogen, oxygen, and water, an ion exchange membrane disposed between catalyst electrodes, and metal screens which support the ion exchange membrane and form the chambers. Referring to FIG. 1 which is illustrative of a common water electrolyzer component arrangement, a first metal screen set 1 which forms the anode chamber is located above the catalytic anode electrode 7 which intimately contacts the ion exchange membrane 5. The opposite side of the ion exchange membrane 5 intimately contacts a catalytic cathode electrode 9, which lies above a second metal screen set 3 which forms the cathode chamber.
During operation, water enters the anode chamber formed by the first metal screen set 1. The water passes through the first metal screen set 1 and intimately contacts the anode electrode 7. At the anode electrode 7, electrolysis converts the water to hydrogen ions and oxygen. These hydrogen ions migrate across the ion exchange membrane 5 while the oxygen passes through the first metal screen set 1, enters the water stream, and exits the electrolyzer 10. Once across the ion exchange membrane 5, the hydrogen ions form molecular hydrogen at the cathode electrode 9 and exit the electrolyzer 10 through the second metal screen set 3. This reaction mechanism is shown in FIG. 1, mechanism A.
The metal screens of the water electrolyzer perform numerous functions. Generally, a low pressure gradient is permitted across the ion exchange membrane within the electrolyzer in order to simplify the system pressure controls. Often, up to about 200 pounds per square inch (psi) of pressure exists across the ion exchange membrane during electrolyzer operation. Since the ion exchange membrane possesses low structural integrity, the pressure gradient across the ion exchange membrane can cause failure thereof. Therefore, the metal screens are used to provide structural support to the ion exchange membrane during operation. These metal screens also form flow paths for the water, oxygen, and hydrogen, and they conduct electrons utilized during the water electrolysis to and from the electrodes, into adjacent cells, or to external circuits.
Although a water electrolyzer utilizing the configuration described above forms a performance stable base line cell at 1000 amperes per square foot (ASF) and 120.degree. F., higher pressure differential operation is desired. Operation at higher pressure differentials will simplify the electrolysis process in many ways including simplification or elimination of pressure control equipment and lower pressure components (on one side). However, under increased pressure differentials, the metal screens fail to provide the necessary structural integrity to the ion exchange membrane. At pressure differentials exceeding about 400 psi, the ion exchange membrane can extrude into the metal screen located on the side of the ion exchange membrane having the lower pressure, thereby causing electrolyzer failure. Referring to FIG. 2, operation above about a 10 psi pressure gradient can deform the ion exchange membrane 5 and force it into the metal screen set 1 on the side of the ion exchange membrane 5 having the lower pressure.
What is needed in the art is a water electrolyzer which is capable of operation at high pressure differentials.